1. Field of the Invention
The invention relates to a continuously variable transmission that changes speed ratios continuously (i.e., in a non-stepped manner). More particularly, the invention relates to a continuously variable transmission that is provided with a primary pulley and a secondary pulley that are hydraulically operated, and a drive belt that is wound around those pulleys and transmits power.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-249132 (JP-A-2005-249132) describes one related continuously variable transmission that is provided with a primary pulley, a secondary pulley, and a drive belt. The primary pulley is formed of a driving-side fixed sheave that is fixed to a drive shaft, a driving-side movable sheave that is provided on the drive shaft so as to be able to move in the axial direction, and a driving-side cylinder member that defines a driving-side cylinder to which hydraulic fluid is supplied. The secondary pulley is formed of a driven-side fixed sheave that is fixed to a driven shaft, a driven-side movable sheave that is provided on the driven shaft so as to be able to move in the axial direction, and a driven-side cylinder member that defines a driven-side cylinder to which hydraulic fluid is supplied.
In this continuously variable transmission, the driving-side cylinder member includes a partition wall member that is fixed to the drive shaft and divides the driving-side cylinder into a sheave-side cylinder that is defined by a driving-side movable sheave and a member-side air cylinder that is defined by the driving-side cylinder member. The driving-side cylinder member also includes a pressing member that divides the member-side cylinder into a member-side hydraulic cylinder that is defined by the driving-side cylinder member and a member-side air cylinder that is defined by the partition wall member inside the member-side cylinder. This pressing member is supported by the partition wall member and the driving-side cylinder member so as to be able to move in the axial direction, and pushes the driving-side movable sheave in the axial direction using the hydraulic pressure inside the member-side hydraulic cylinder.
Further, the drive shaft has a first drive shaft internal fluid passage that is open at the outer peripheral surface of the drive shaft to supply hydraulic fluid to the driving-side cylinder, and a second drive shaft internal fluid passage formed away from the first drive shaft internal fluid passage in the axial direction. The driving-side movable sheave has a sheave internal fluid passage that communicates the first drive shaft internal fluid passage with the driving-side cylinder. The partition wall member has a partition wall internal fluid passage that communicates the driving side cylinder with the member side hydraulic cylinder. According to this structure, when the driving-side movable sheave is moved away from the driving-side fixed sheave, hydraulic fluid is supplied from the first drive shaft internal fluid passage of the drive shaft into the driving-side cylinder through the sheave internal fluid passage, and then supplied from the driving-side cylinder into the member-side hydraulic cylinder through the partition wall internal fluid passage.
Meanwhile, when the driving-side movable sheave is moved toward the driving-side fixed sheave, hydraulic fluid is supplied from the second drive shaft internal fluid passage of the drive shaft directly into the driving-side cylinder, and then from the driving-side cylinder into the member-side hydraulic cylinder through the partition wall internal fluid passage. In this continuously variable transmission, providing a so-called double piston structure that moves the driving-side movable sheave using the hydraulic pressure inside the driving-side cylinder and the hydraulic pressure inside the member-side hydraulic cylinder increases the pressure on the driving-side movable sheave, which increases the squeezing force on the drive belt from the driving-side movable sheave and the driving-side fixed sheave, and thus increases the power that is transmitted.
However, in this related continuously variable transmission, the sheave internal fluid passage that communicates the first drive shaft internal fluid passage formed in the drive shaft with the driving side-cylinder is formed in the driving-side movable sheave. This driving-side movable sheave has an inner cylinder portion that slides along the outer peripheral surface of a primary shaft that serves as the drive shaft, a radially extending portion that continues from the end portion of the driving-side fixed sheave of that inner cylinder portion and extends toward the outer peripheral side, and an outer cylinder portion that continues on from the outer peripheral end of this radially extending portion and extends axially in the same direction as the inner cylinder portion, just as described in JP-A-2005-249132.
Therefore, when forming the sheave internal fluid passage in the radially extending portion, a drilling tool is set angled toward the radially extending portion from between the inner cylinder portion and the outer cylinder portion, and the sheave internal fluid passage is machined through the inner peripheral surface of the driving-side movable sheave at an angle from the surface of the radially extending portion, so the drilling process is a lot of work. Also, the drilling process produces burrs on the inner peripheral side of the through-hole, and the process to remove these burrs is troublesome.
Moreover, an annular notch is formed in the outer peripheral surface of the primary shaft in order to reliably communicate the angled sheave internal fluid passage with the first drive shaft internal fluid passage formed in the drive shaft. Therefore, both the process of forming this annular notch and the process of removing the burrs take time and effort. In addition, the partition wall internal fluid passage that communicates the driving-side cylinder with the member-side hydraulic cylinder is formed in a corner portion of the partition wall member, and the processes of drilling the hole and removing the burrs also take time and effort. As a result, the number of processes for forming the fluid passages that supply hydraulic fluid increases, so the production efficiency decreases.